I know you're supposed to keep nutrient out of direct light. Not just to prevent agea growth, but also for making sure some items in the nutrient do not become unstable/modified by the light.

I am concerned if I set up my system correctly. Each time the tray floods, the nutrient will be inundated with light from the grow light hanging above (my system has net pots setting in a flood tray, so there is open space where the nutrient is directly under the light).

Could anyone please tell me how much of a problem this is?

Also I am considering cutting some black and white poly film and putting holes in it to set the net pots down in - might help solve the problem, if there is a problem here at all. Would also help to reflect light back up to the plants (with the white side of the black/white poly facing up).

Thank you anyone for your advice!

The thing about algae (green types) is that it produces oxygen while the lights are on but depletes oxygen during dark cycles. If we were to leave our lights on for 24 hours it would benefit to a degree until it became chocking to the system. Best to not allow it at all as much as possible.